Use ghcr address as registry ref in docker build cache-to

[AdrianDAlessandro]

Description

This PR implements the suggested fix by @davehorsfall to fix the bug with deployed images not working. I think this is what you meant, Dave...

Fixes #723

Type of change

• Documentation (non-breaking change that adds or improves the documentation)
• New feature (non-breaking change which adds functionality)
• Optimization (non-breaking, back-end change that speeds up the code)
• Technical work (non-breaking, change which is work as part of a new feature)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (whatever its nature)

Key checklist

• All tests pass (eg. python -m pytest)
• The documentation builds and looks OK (eg. mkdocs serve)
• Pre-commit hooks run successfully (eg. pre-commit run --all-files)

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added or an issue has been opened to tackle that in the future. (Indicate issue here: # (issue))

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[AdrianDAlessandro]

@sbland We need to get this PR merged before we can deploy any new releases. So if you want your new features live, I'll need an approving review. I'm not confident enough of my understanding of docker manifests, etc to merge this without a second opinion

[Copilot]

Pull request overview

This PR updates the GitHub Actions Docker build/publish pipeline to avoid overwriting published GHCR image manifests with BuildKit cache artifacts (the root cause described in #723). It does this by moving the BuildKit registry cache to a dedicated :buildcache tag and pinning the published image platform to linux/amd64 for Azure compatibility.

Changes:

• Write BuildKit cache-to to ghcr.io/<owner>/<repo>:buildcache instead of using the application image tag(s).
• Add cache-from to read from both GHA cache and the dedicated GHCR :buildcache tag.
• Set platforms: linux/amd64 for the docker/build-push-action invocation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
.github/workflows/publish.yml	Renames the publish step label to reflect that it publishes (no behavior change).
.github/actions/docker-build/action.yml	Moves registry cache to a dedicated :buildcache tag and pins build platform to linux/amd64 to prevent manifest corruption and improve deploy compatibility.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.